Isosceles Triangle Theorem
If two sides of a triangle are congruent , then the angles opposite to these sides are congruent.
Let be the midpoint of .
Join and .
Since is the midpoint of , .
By Reflexive Property ,
It is given that
Therefore, by SSS ,
Since corresponding parts of congruent triangles are congruent,
The converse of the Isosceles Triangle Theorem is also true.
If two angles of a triangle are congruent, then the sides opposite those angles are congruent.
If , then .